The term “hybrid vehicle” typically refers to a vehicle that has both internal combustion and electric motor propulsion. In a conventional hybrid vehicle, a first clutch is installed between an internal combustion engine and an electric motor/generator, and a second clutch is installed between the motor/generator and the driving wheels. By such configuration, the conventional hybrid vehicle can provide two driving modes, that is, a hybrid drive mode and an electric drive mode. In the hybrid drive mode, the first and second clutches are engaged so that the vehicle may be driven by a torque generated from the engine and/or torque generated by the electric motor/generator. In the electric drive mode, the first clutch is disengaged and the vehicle is driven by a torque generated from the electric motor/generator only. By way of example, Japanese Patent Laid-Open Publication No. Hei 11-82260 discloses one of such conventional hybrid vehicles.
When the vehicle is in the electric drive mode, fuel to the internal combustion engine may be cut off, thereby improving fuel economy. In this application, the fuel cut off will be referred to as “defueling” the engine. However, when switching from the hybrid drive mode to the electric drive mode, the order between the engine defueling and the first clutch disengagement tends to affect the quality of driving.